Schistosomes are parasitic flatworms that cause a chronic, debilitating disease afflicting over 200 million people in over 70 countries. The parasites live for years, sometimes decades, in what should be a very hostile environment - the blood of vertebrates - yet they appear to solicit little if any protective reaction from two of the host's major defensive systems: the hemostatic system and the immune system. We hypothesize that proteins at the host-interactive surface are central to the parasites ability to dampen host immunity and hemostasis while, at the same time, permitting metabolite exchange. In this competing renewal, we propose to use new molecular methods such as RNA interference that were first developed for use with schistosomes under our previous grant, RO1 AI056273, to test several key hypotheses concerning: 1) the role of tegumental ecto-enzymes in hemostasis and immunomodulation, 2) the ability of tegumental sphingomyelinase to alter permeability properties at the parasite surface, and 3) the molecular mechanisms of trans- tegumental metabolite exchange. The functional genomics approach we adopt here coupled with independent and direct, follow-up experiments employing more traditional cell biology and biochemistry techniques are designed to provide significant new information concerning the schistosome host interactive surface. In addition the work is designed to identify tegumental proteins critical for parasite survival in the host and subsequent screens will be undertaken to discover drugs that inhibit these molecules. In this way, our planned experiments have the potential to reveal novel and valid targets, as well as new treatments, for intervention in a parasite that remains a widespread and major cause of human disease.